


A Song of Sin and Desire

by liliumweiss



Category: Once Upon a Time (TV)
Genre: Alternate Universe - Supernatural Elements, Captain Swan Supernatural Summer 2020 (Once Upon a Time), F/M, Siren!Emma, devil!Killian
Language: English
Status: In-Progress
Published: 2020-08-20
Updated: 2020-08-20
Packaged: 2021-03-06 17:53:33
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 3,384
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/26012917
Author URL: https://archiveofourown.org/users/liliumweiss/pseuds/liliumweiss
Summary: It's her voice that captures him first, that siren song he cannot forget.Centuries later, he's still looking for that voice, for the woman it belongs to, and against all odds, he won't give up.He's the Devil, after all.It's the darkness inside him that lures her to him, a force ready to consume her.That warning, that omen, it means nothing to her now that she's found him, now that she can't, that she doesn't want to escape him, not even when strange forces are working in the dark to bring hell on earth and destroy life as she knows it.But what they don't tell you in children's books, is that mermaids are not meek creatures.When they hunt, they hunt to kill.
Relationships: Captain Hook | Killian Jones & Emma Swan, Captain Hook | Killian Jones/Emma Swan
Comments: 6
Kudos: 24
Collections: Captain Swan Supernatural Summer 2020





	A Song of Sin and Desire

**Author's Note:**

> Whew, another story? Yup! You know me, I can’t stay away from the beauty that is @cssns and those lovely ladies ♥ This year, I have to thank the amazing @carpedzem for the prompt that set things into motion, and this fic wouldn’t be what it is set to be without @shardminds and her yelling the plot right along with me. Of course, all the people in the discord chat who supported me are to thank for this fic, and I can’t absolutely forget @demisexualemmaswan for her beta skills and @artistic-writer for the AMAZING art that will be posted in a while, and y’all, it’s bloody fantastic.
> 
> This fic is somehow a Lucifer AU (and the fact that s5A will come out tomorrow is not lost on me!) but with a touch of more supernatural related stuff, which will come into play in the future chapters. It will be E rated for sexual content and a bit of violence - and really, the title speaks for itself, but I know how much triggers and warnings are important.
> 
> I hope you enjoy ♥

_The Caribbean Sea, 1718_

Warm sunlight washed upon her, the scales of her tail glittering, capturing the attention of every sailor who had the luck to cast his eyes upon her figure.

The creature smirked, watching the sun behind her eyelids, but her grin faded quickly.

Truth to be told, unlike the majority of her sisters, this particular siren didn’t enjoy killing humans or any other creature. Sometimes, however, she did enjoy toying with them, especially whenever they insulted her or were extremely ruthless. After all this time, she could recognize them by their odor, they smelled just like death, rotten to the core.

The fragile-looking yet sharp tips of her fins brushed the water surface, disturbing it, desperately trying to hunt away her boredom.

She longed for the night, just after the sunset, when the sky was a myriad of colours still and she allowed herself to wrap the bracelet around her wrist and her tail to become human legs.

Against her own nature, this mermaid loved to mingle with human beings and other creatures, never one to be confined to the sea, no matter how much she loved and needed it. She’d always been one to defy the rules, but it had been her voice the main reason she’d first come in contact with other creatures.

The very first one she attracted, many eons ago, had been a woman with the skin of a lizard and the tongue of a snake - both figuratively and not. Nimue was her name, but it wasn’t her spirit that ruled her mind.

Scared, the mermaid had swam away as if the Leviathan itself was chasing her. Never before had she seen such darkness, and it’d scared her so much she stopped singing for weeks, worrying her clan, for sirens need to sing as much as a human being needs to breathe.

But not all the creatures she attracted were foes. Many had become her friends, strange as it was. Alas, said friends were now occupied elsewhere.

Different from her clan, she missed her friends and would never find their presence annoying. Her so-called sisters, on the other hand, were extremely stubborn, some more lethal than others, even, which was the main reason why they disagreed pretty much on everything and what pushed Emma to search other people's company.

Given how clans were built, she couldn't just leave it, not even if she wanted to: not only the leader of the clan wasn't easy to get along with, but a mermaid needed to stay close to her kin.

Emma, however, was nothing if not resourceful, and she had, after all, thought about a plan to get away safely.

It had been the story of a siren living in the waters north of Denmark to plant the seeds of this insane idea.

Well, insane for any other mermaid, of course. It had taken her decades to find the magical bracelet, having to stop for long periods of time, even, so she wouldn’t arise any suspicion. At last, it was her voice that allowed her to bargain with a witch for key information. And now, the bracelet was her most precious possession.

True, the siren she’d heard of traded her life in the sea for love, something Emma had never experienced, but Emma was trading it for her own freedom and happiness. Both her reasons and the infamous redhead’s were valid.

_Soon_ , Emma sighed to herself, a shiver of excitement running down her spine.

Many were the years she’d spent walking among humans, her first attempts at standing quite comical. At first, when she didn’t know how to act, trying to copy what she saw other humans do, the sea had been her refuge from many wrongdoers. She might not know much about human beings, but she knew how the world went, how people could be good, but also bad.

Good and evil were two concepts she was familiar with, being a siren didn’t prevent sirens from acting either way. Mostly, her kin was conceived as evil creatures luring men to their death, which, admittedly, was true, and so they _were_ evil, but among them, there were sirens with a conscience, sirens who didn’t want to cause people to die just because it was their nature.

Emma wanted to see the world, she wanted to be free of the idea that _she_ was evil. For years, as she wandered around the streets of the Caribbean islands, mingling with the folk and singing for them in taverns, she had come to know many people, people who treated her well and with respect, something she rarely experienced in her clan.

Given her immortal life, Emma knew she couldn’t find a family for herself, but she could still create bonds of friendship with someone, balancing her need to be included in a clan with her desire to be free. If anything, having even just one friend had shown her what being treated well, what being _loved_ meant.

Her first lover had been a pirate.

She didn’t fall for him for his beauty or anything, she didn’t fall at all, but she still loved him. He’d been gentle, rough, lustful and romantic, sometimes all at once. Charles Vane had never treated her bad, the agreement that they would seek comfort in one another and nothing more always respected by both of them. Oh, he loved her, aye, but his heart belonged to another, yet Emma still took what he had to offer her, for it was enough for her. In a way, though, part of his heart would always belong to her, as hers would him.

He became part of the reason why she wanted to leave: there were good men among those her kin killed, there were young boys, girls disguised as men, and yet no one in her clan was remorseful, shrugging it off and blaming their nature. How could such an intelligent species be so stupid?

Emma sighed, rubbing her cheek on the hard rock, inhaling the scent of salt as the sun warmed her skin, making it itch as the seawater evaporated. She hummed in delight, soaking in the warmth of the sun and the stone, her tail curling just beneath the water in bliss.

Unless they were hunting, the life of a siren was pretty boring. Oh, right, unless they were part of royalty or loved politics. There were supernatural beings all over the world, and though they were being kept a secret from mere human beings, territories had to be defined and peace had to be kept. Besides, there were many creatures who loved to, hmm, _mingle_.

Emma had heard of places where vampires drank fae’s blood, where witches and warlocks cast spells on willing creatures to heighten their pleasure. The memory of those whispers brought a blush to her cheeks.

Truth to be told, aside from Charles, she’d never had another lover. Many had tried to lure her into the inn’s beds, but she’d never fallen for it, always wanting more from a man, something only her pirate had been able to give her. More than, she wanted to experience what the stories were all about, what a vampire could do to her while her blood filled his mouth or what new sensations a warlock could make her feel. And wolves, hmm, wolves were just so passionate Emma had heard murmurs that made her tremble.

A trembling sigh fell from her lips. She licked them, finding them dry, her mouth parched, throat itching with the need to _sing_.

Tracing the valleys of the rock, she started humming, the melody filling the air immediately, irresistible to her ears as well. Many creatures had pointed out how captivating her voice was, how they found themselves brought to her knees in front of her, completely at her mercy.

At least, this only counted for those who didn’t want to actually capture her voice for some spell or just capture _her_.

Admittedly, she’d been lucky to escape every time, especially that first time, when Nimue manifested herself.

Her voice wavered at the memory. Emma squeezed her eyes, pouring more of her own magic in the song, the melody changing from a passionate one to one yearning for freedom, freedom from darkness and the binds of her kind.

The last note had yet to create a ripple on the water that a clapping sound reached her ears.

Twisting on the spot, she hissed at the newcomer. Whoever it was, she wouldn’t be able to fight them above water, but she could distract them long enough to escape. It was a coward move, but in the water, only the fastest one to escape survived if they couldn’t face the beasts lurking in the darkness of the abyss.

Her green eyes focused on the man standing ankles deep in the water, waves lapping at his calves, soaking his breeches. He was tall, his shoulders broad, a trait that was enhanced by the way he crossed strong arms over his chest.

_Warrior_ , that was what Emma saw oozing from him, the innate strength of a warrior, but _more_. Bright blue eyes shone beneath the sun, the rays casting a glow around his entire figure, almost like… like a halo.

Emma blinked in surprise, relaxing just a touch. The being in front of her very eyes might be an angel - she wasn’t completely sure since she’d never met one, but his power… - but it didn’t mean he wasn’t a threat.

They stared at one another for interminable minutes, the only noises the gentle rolling of the waves upon the nearby shore and Emma’s slowly calming breath. Deep within her, Emma knew she couldn’t escape him, not if what they said about them, that they were capable of slowing time, was real. She gulped, swallowing her rising interest in him, in the unknown, and the increasing want to see his wings.

Clearly, after all these years, saltwater was affecting her brain.

Emma raised her chin, sharp teeth still bared in a snarl. Not the prettiest view, but she’d never been one to care more about appearances than her own life.

«No need to be so on edge, my lady.»

Her eyebrows shot up high on her forehead. «It is not every day that an angel interrupts a siren’s song.» While she sounded sweet, she felt anything but toward the being in front of her.

He conceded a small smile of his own, lips twitching in amusement. «My apologies,» the stranger told her, and she did recognize a tiny bit of apology in his voice. Mostly, there was annoyance, amusement and a faint note of wariness. Why that was, though, she did not know.

Squinting, Emma tilted her head to the side, her long, sun-dried hair covering her bare breasts. It was common for sirens to wear nothing to hide their upper bodies, they weren’t shy; besides, it helped them with the task of luring men to their death.

Still, Emma wasn’t fond of baring herself to anyone who wasn’t her lover. Charles had treated her like a goddess, and what was more important, he’d never complimented her so she would fall into his bed; the man never spoke lies, not to her. A siren’s ability didn’t stop to their own voice, but they could hear what most wouldn’t, and so they were capable of knowing when a person was lying.

«May I know why would an angel-»

«Archangel, actually.»

Emma pursed her lips in a tight line, her patience wearing thin, all formalities lost. «Why are you here?» And now it had dissolved like smoke.

The angel tilted his head, his lips twitching again. «You have a marvelous voice,» he began, his flattery making Emma arch her brow.

«Many do tell me so, although they compare it to an angel’s song.» Emma smiled sweetly up at him, blinking almost seductively. «Do you sing, _archangel_? Perhaps with the aid of a harp?»

Teasing a mystical creature? Emma truly had a death wish.

The smile broke on the angel’s face, and he dropped his head, laughing to himself. His chuckle was warm, lovely even. _Angelic_ , her mind supplied, at which she rolled her eyes at herself. There was no denying it, though: sirens only dreamt to have such a laugh. True, theirs were enchanting, but nothing compared to what she’d just heard.

«I’m afraid I don’t know how to play a harp. Perhaps one of my sisters, but I wouldn’t risk enraging her, she’s quite… susceptible.»

Emma tilted her head, fins swishing in the shallow water. «Unlike you?»

«After millennia, I have learned how to be patient when faced with challenges such as yourself.»

She lifted her chin, curiosity winning over the need to taunt the archangel. «And why would I be a challenge? Unless my entire kin is a threat to someone, that is. It’s nice of you to warn me before you end my existence.»

Joking about her imminent death? Perhaps she’d spent too much time around Charles and pirates in general.

Beneath the creature’s blazing blue eyes, Emma took a shaky breath, nails as sharp as broken shells digging into the rock at her sides, the stone giving in under her attack. This was no darkness-ruled witch, nor a horny faun, no. This was a predator in disguise, his human vessel a way not to be noticed among simple humans. Legends talked of giant bodies of light, some talking about them eclipsing the sun itself, others spoke about how a million eyes looked down upon them from the feathers adorning their wings, but Emma doubted those stories to be true, for nobody ever looked at an angel and lived to tell the story.

«I wish I could say you are no threat to me or the whole world, but I’d be lying, and if there’s something I don’t tolerate, is lies. As for your kin, I may not agree with their murderous ways, but alas I’m not here to change the balance of the world, as it is not in my power, nor it is my duty to do so.»

Against her better judgement, Emma was… _fascinated_.

Since she’d first discovered there were different beings other than humans and sirens, Emma had wanted to learn more about them, about their magic and characteristics. Wielders of magic were the most fascinating, in her modest opinion, for they were capable of conjuring anything out of thin air. Or rather, not quite, as the many who’d crossed her path had taught her, but the principle remained the same, as did the effect they had on her.

The few vampires she met had requested a taste of her blood, but she knew better than give into their desires, although Emma wasn’t exactly opposed to the idea now. After all, it had been a good fifty years since they last propositioned to her.

Werewolves were even more rare to come in contact with, and they usually didn’t ask anything from her other than a song, but one of them had given her the most beautiful compliment ever.

« _Not even the moon can even compare with the call of your voice_.»

It still sent tingles traveling down her tail.

Mostly, she attracted faes of every sort and element, even those fueled by fire.

Emma shook her head. «I beg your pardon, but what do the likes of you want with me?»

The archangel moved his shoulder as if he were shrugging, but it was different, as if the human dress he’d chosen for himself was a bit too tight. Differently from common belief, they didn’t inhabit actual human beings, but they used their power to assume human-like features.

Again, Emma had to swallow the question that was bubbling up inside her, the intense need to know how they chose which characteristic they wanted for themselves almost slipping past her lips.

«I was sent here to warn you, Emma.»

The tone he used didn’t promise anything good; it had Emma on edge, her most basic instincts telling her to swim as fast as she could as far away as possible, even knowing that he would find her.

Biting her cheek until she tasted blood, Emma narrowed her eyes slightly, and tilted her head.

The angel mirrored her position, as if he were trying to learn more about how humans acted, those little gestures that couldn’t be taught. In that moment, Emma realized that even if he might appear human, he wasn’t, not even in the slightest, and she didn’t want to know how much that difference extended to feelings or sense of honor.

«You were?»

A warning from a celestial being… Emma swallowed, her throat strangely dry.

Her mind began to wander. Was it because of the deaths, because her kin killed too many humans? Then why come to her? Why not speak to her leader? It didn’t make any sense, and that scared her even more.

«I’ve been observing you for a while, your rendezvous with other creatures didn’t go unnoticed.»

At that, Emma raised her eyebrows and snorted. «So you’ve descended from Heaven-»

«The Silver City.»

Emma rolled her eyes. «From the Silver City to chastise me over encounters with other supernatural beings, some of which are my _friends_?»

A grimace appeared on his handsome face. Despite his unnerving attitude, Emma couldn’t deny how fascinating he was. Or at least, how fascinating his _human dress_ was. _Uh_.

«I apologize, my lady, poor choice of words.»

If possible, her eyebrows rose even closer to her hairline. _Is that so?_

Clearly uncomfortable with the situation, the angel shifted his weight from one leg to another. «Differently from your kin, you’ve attracted many creatures, not only humans, and definitely not for evil purposes. In fact, I don’t even believe you do that on purpose.»

Emma couldn’t help but laugh bitterly. «I do not know how old you are, _darling_ , but I’ve never harmed someone who didn’t deserve it.»

«Again, you’ve misinterpreted my words.»

A hiss escaped her, teeth clicking together and eyes storming. «Then stop talking in riddles, _angel_. My patience is wearing thin.»

Barely suppressed rage rippled beneath his features; clearly, he wasn’t very much patient either. Fear engulfed Emma, but she forced herself to keep her brave mask on. Too easily she forgot how powerful an angel was.

He took a step forward, the water not even moving. Emma gulped, reminded once again that he wasn’t a mere supernatural being. «How many times have you been visited by creatures filled with darkness? How many have asked for your voice, for your power? Not for your blood or for a night between your thighs, but for what makes you so unique. You know who I’m talking about, don’t you, _love_?»

Utter terror settled deep inside her bones. She remembered well, Nimue’s darkness almost managing to catch her.

She licked her dry lips. «Aye, I do.»

«Then you know what dangers you might encounter, Emma.» His voice seemed to increase volume with every word, the sound reverberating through her. «I’ve been sent here to tell you to be careful with your voice. There are more dangerous evils lurking in the darkness than a sorceress whose soul has been sold to gain power. Your beauty and the vastity of the ocean won’t always help you.» As he spoke, he moved until the fabric of his breeches brushed the scales of her tail; every attempt to shy away from the touch was futile. He bent forward, blue eyes blazing with fire - or was it his true essence? «Mark my words, Emma, evil will find you again, and pray my Father that you’ll be able to escape its clutches once again.»

In a blink, he was gone.

The rush of the waves came back to her ears, their sound almost deafening. Emma let out a trembling breath, tears pooling in her eyes as her chest heaved with anxiety.

A fish swam right next where the fins of her tail rested beneath the water, making her flinch.

_Gods_ , she whimpered to herself, worrying her lower lip until she tasted blood.

The angel’s words echoed in her mind, increasing her fear. She wished he’d not come at all, that he’d let her bask in her ignorance until the darkness came, for not even the water felt safe now.


End file.
